Has Sweden been attacked before?

The most recent attack in Stockholm was in, 2010, when an Iraqi-born Swede killed himself while detonating two bombs days before Christmas, which failed to cause any other fatalities.

Taimour Abdulwahab al-Abdaly, who studied at the University of Bedfordshire and lived in Luton for almost a decade, supported al-Qaeda and named his son after Osama bin Laden.

He used a car bomb and pipe bombs in the explosions at the intersection of Bryggargatan and Drottninggatan, near Friday’s attack.

Minutes before the blast, an email threat had been sent to Swedish security services, referring to the country’s troops in Afghanistan and cartoons depicting the Prophet Mohamed, and his wife later uploaded audio messages to YouTube.

There have been several other plots in Sweden, which saw a suspected Isis supporter arrested after planning a pressure cooker bombing in February 2016.

A separate plot in 2011 was to target an art festival in Gothenburg to be attended by a Swedish artist who had drawn controversial cartoons of the Prophet Mohamed, with three men charged with intending to stab him to death.

Isis claimed responsibility for a firebombing in Malmö in October at a building used as an assembly hall by Shia Muslims.

The group has declared the sect apostates and targeted followers with terror attacks around the world, but no one was injured in the Swedish attack.

A 30-year-old Syrian man was charged with terror offences over the arson attack last month, after prosecutors found he had affiliated himself with Isis.

(Getty Images)

Is there a high terror threat in Sweden?

The national threat level has been set at number three - “elevated” – on a scale of one to five since 2010.

The Foreign and Commonwealth Office said there was a "general threat from terrorism" for British travellers and urged people to follow police advice and temporarily avoid central Stockholm.

Earlier this year, the head of the country’s counter-terror force said the biggest threat emanated from “lone wolves” inspired by Islamist groups including Isis and al-Qaeda.

“The biggest risk we're seeing is the individual player, who has been inspired and perhaps radicalized, almost on their own,” said NCT head Mats Sandberg.

“In our view that risk is greater than a major coordinated attack with several actors similar to Paris for example.”

Around 140 Swedish foreign fighters are believed to have returned from Syria and Iraq, out of at least 300 who travelled to the region to join Islamist groups.

The country is believed to have one of the highest Isis fighters per capita in Europe, although it sits far behind France, the UK, Belgium and Germany in terms of numbers.

Methods of dealing with returning jihadis has been a subject of fierce as the terrorist group continues to lose territory across Syria and Iraq, with fears of an influx of militants fleeing a major offensive in Mosul.

Around one fifth of the group’s militants – 3,700 people – are residents or nationals of Western Europe, a King’s College London study estimated last year.

(Reuters)

What effect has the attack had across Europe?

Public transport in Stockholm has been shut down, with disruption expected on international train services and at airports.